1. Field of the Invention
The present invention relates to test equipment for asymmetric digital subscriber lines (ADSLs).
2. Background of the Invention
Asymmetric Digital Subscriber Line (ADSL) technology is a high speed transmission technology that uses existing copper wire pairs from the telephone company""s central office (CO) to provide high-speed data transmission to equipment at the subscribers"" premises. ADSL uses a central office ADSL transceiver unit (ATU-C) and a remote transceiver unit at the subscriber""s premises (ATU-R) to send high speed digital signals down the copper wires. ADSL is asymmetric, because it is designed to send information at a faster rate downstream (from the CO to the subscriber""s premises) than upstream (from the subscriber premises to the CO). In the downstream direction, ADSL may be used to provide data rates ranging from 256 Kb/s to as high as 6 Mb/s, depending on the local loop. In the upstream direction, ADSL may be used to provide data rates ranging from 128 Kb/s to as high as 800 Kb/s, again depending on the local loop.
As described above, ADSL service is provided using the same outside plant (OSP) cable pair that is used to provide normal plain old telephone service (POTS), i.e., normal telephone voice service, to a customer. There is normally no interference between the voice service and the ADSL service, because ADSL uses frequencies that are well above the voice band. ADSL service is provided to a customer by installing a Digital Subscriber Line Access Multiplexer (DSLAM) at the main distribution frame (MDF) to combine the ADSL signal with the voice signal. The main distribution frame (MDF) is the apparatus that connects the telephone lines coming in from outside the CO to the internal lines in the CO. The MDF normally includes protective devices.
Specifically, ADSL service is provided by removing the jumper that otherwise connects the OSP termination to the office equipment (OE) termination, and then connecting a DSLAM to the OSP and OE termination. As shown in FIG. 1, jumper 121 is used to connect OSP termination 101 to terminal 103 of DSLAM 104, and jumper 120 is used to connect OE termination 102 to terminal 105 of DSLAM 104. Within DSLAM 104, the data signal from the Asynchronous Transfer Mode (ATM) network 106 is transmitted by ATU-C 108, using the ADSL transmission scheme. Similarly, the ADSL signal from ATU-R 114 is received by ATU-C 108, and the data from the customer is sent into ATM network 106. The signal is combined with the voice signal from voiceband switch 108. Splitter card 109 is essentially a low-pass filter that prevents the ADSL signals from reaching voiceband switch 107. The combined signal is then fed to OSP termination (or terminal) 101 via lines 110, terminal 103 and jumper 121.
Outside the MDF, the conventional OSP cable pair 111 now carries both ADSL and voice signals. At the customer premises, a splitter 112 (which is also a low-pass filter) blocks the ADSL signals from reaching the customer""s telephone 113 or other device. The ADSL signals are transmitted to ATU-R 114 over lines 115, i.e., over the cable pair to the end-user""s premises. Dashed line 116 represents the interface between the telephone network and the customer""s premises.
The ADSL service can possibly fail, either because of faulty installation, or because the outside cable pair is simply not capable of carrying the higher-frequency ADSL signal (for example, because that cable pair is loaded down with spaced inductors). For that reason, telephone service providers usually test the ADSL installation prior to putting the ADSL in service.
The present invention is an apparatus for testing the installation and operation of ADSL service at a Central Office. With the test apparatus electrically connected to a cable pair at the main distribution frame at the CO, an ATU-C and an ATU-R in the test apparatus are used to test synchronization with an end-user""s ATU-R and a CO""s ATU-C, respectively. A voltage detector in the test apparatus starts the test automatically when it detects a voltage applied by the CO across the lines connecting the testing apparatus to the CO.
The ATU-C and an ATU-R are mounted on a test platform, together with the voltage detector and a load coil detector. The load coil detector checks the cable pair for the presence of load coils (which, if present, would render ADSL service inoperable). The ATU-C in the test apparatus can also determine the connect speed of the end-user""s ATU-R.
When not in use, i.e., when the test apparatus is idle, the ATU-C and ATU-R are connected to each other and are synchronized to each other, so that the testing technician can test them against each other to make sure that they are operating properly prior to conducting any tests of the ADSLs.
In a preferred embodiment of the present invention, when the technician connects the test apparatus to the circuit, the voltage detector in the test apparatus detects the voltagexe2x80x94applied to all POTS lines by the COxe2x80x94and initiates the test by automatically throwing a four-pole double-throw switch from the idle position to the testing position to initiate the test.
The present invention is preferably implemented using test shoes and test jacks at the main distribution frame. Using the existing main distribution frame test shoes and test jacks provides four-wire access to the ADSL infrastructure, so that the test platform can xe2x80x9clook outxe2x80x9d toward the end-user as well as xe2x80x9clook-inxe2x80x9d toward the office (i.e., the DSLAM in the case of ADSL). This provides the capability for deploying both an ATU-C and an ATU-R. This has two advantages. First, it allows the CO technician to test the wiring infrastructure at the CO, and also to obtain an indication of the end-user""s connect speed. Second, it allows the test ATUs to remain logically connected when not in use, which provides known-good units, whenever such units are needed for a test. The connection towards the end-user also allows the use of the test apparatus as a convenient platform to house a load coil detector, which could check for the presence of load coils on the cable pair while the ATU-C attempts to synchronize with the end-user""s ATU-R.
Accordingly, it is an object of the present invention to provide an apparatus and method for testing the installation of ADSL service over POTS lines.
It is also an object of the present invention to provide a two-way test of ADSL installations, that tests the wiring and apparatus at the central office and the wiring and apparatus at the end-user""s location.
It is a further object of the present invention to test for the presence of load coils in outside line cable pairs.